The present invention relates to a wireless type tire status monitoring apparatus capable of checking the status of a tire, such as tire air pressure while the driver remains in the vehicle. More particularly, this invention relates to a tire status monitoring apparatus which has a transponder which transmits data indicating the status of a tire in response to a request signal and a transceiver which transmits the request signal and receives data sent by the transponder.
There are tires each incorporating a transponder having a coil antenna for radio transmission of the status of the tires of a vehicle. In the case where a request signal is transmitted from outside, the transponder transmits the identification of the associated tire and other data via the coil antenna based on power induced in the coil antenna (see Japanese Patent Laid-Open Publication No. Hei 5-169931).
In the technique disclosed in the above Japanese patent document, however, the time interval for externally transmitting the request signal is constant regardless of the speed of the vehicle. Accordingly, the transponder that responds to the request signal always transmits data for the associated tire at a constant time interval. Even in a case where the driver should be promptly informed of an abnormal state of a tire, such as in fast driving mode. Therefore, the driver would not be quickly informed of an abnormal state.